There exists a mechanism for driving plural and individual components so as to move as a unit by means of plural motors. For example, there exists a vehicle seat, whose state is electrically switchable by using a motor between a seating state for allowing a user to sit thereon and a stored state by which a space within the vehicle is enlarged. Disclosed in JP2007-62507A is an example of an electric seat apparatus. The seat apparatus disclosed in JP2007-62507A is configured so that a state of the seat apparatus is switchable between a seating state and a stored state in response to an operation of an operation switch by a user. More specifically, a seat cushion and a seat back are driven by means of respective motors while the user continuously operates the operation switch, so that the state of the seat apparatus is switched between the seating state and the stored state. In this case, a moving speed of at least one of the seat cushion and the seat back is changed from a corresponding initial moving speed in a process of changing the state of the seat apparatus between the seating state and the stored state. Accordingly, an interference between the seat cushion and the seat back may be avoided and further, a total operation time may be shortened because a moving time of the seat cushion and a moving time of the seat back overlap. According to the above-mentioned mechanism, the motors need to be accurately controlled in conjunction with each other.
In a case where a mechanical end-point is set within a movable range of a movable portion such as the vehicle seat, an impact noise may be generated when the movable portion is mechanically stopped at the end-point or an uncomfortable vibration may be generated if the movable portion reaches the end-point while the motor is rotated steadily. Therefore, a slow down control for gradually decreasing a number of rotations of the motor (a rotational speed of the motor) needs to be executed when the movable portion is moved to the vicinity of the end-point, so that the displacement of the movable portion is slowly stopped. Similarly, in a case where the motor is operated at a steady number of rotations immediately after being actuated, the movable portion may suddenly move or an excessive load may be applied to the motor. Therefore, a slow start control for gradually increasing the number of rotations of the motor needs to be executed in order to start moving the movable portion slowly. However, a total operation time from a start of the operation to an end of the operation is preferably shortened as much as possible even if the movable portion is started to move slowly and is stopped slowly.
Furthermore, a posture of the vehicle seat is not limited to two simple states, i.e. the seating state and the stored state. For example, a reclining angle of the seat back may be adjusted by an occupant while the vehicle seat is in the seating state. In other words, the posture of the vehicle seat when being moved is not fixed to one posture. Therefore, in a case where a control is executed on the basis of a target number of rotations of the motor, which is determined in response to a position of the seat in order to start and stop the movable portion slowly by means of the motor, without considering a position and the posture of the vehicle seat when being started to move, the vehicle seat (plural movable portions) may not be moved in unity and the user may feel discomfort. Hence, a series of operations from the start of the operation to the end of the operation, are preferably executed so as to achieve a unified movement of the vehicle seat without being influenced by the operation starting position of the vehicle.
Furthermore, in the case where the vehicle seat is operated so as to slowly start moving, the number of rotations of the motor is low, specifically at an early stage of the operation. For example, in a case where a system for calculating an actual number of rotations of the motor on the basis of a pulse signal outputted from a hall sensor is adapted, a resolution of the actual number of rotations of the motor may become low while the number of the rotations of the motor is low. As a result, an update of the actual number of rotations of the motor may be delayed. Accordingly, a feedback control based on a deviation between the target number of rotations and the actual number of rotations of the motor may not effectively function. On the other hand, in a case where a simple feedforward control is executed, a great difference between the actual number of rotations and the target number of rotations of the motor may occur because a slide resistance differs depending on a mechanical annual change of the motor, the vehicle seat and the like and on an ambient temperature. As a result, the motor may unexpectedly be stopped because of a shortage of a torque. Hence, the motor is preferably controlled by using a control method having a high tolerance against an operation environment such as the mechanical annual change, the ambient temperature, a power voltage fluctuation and the like.
As described above, specifically in the case where the mechanism is driven by operation of the plural motors in conjunction with each other, each motor needs to be accurately controlled. Therefore, a motor control that overcomes the above-mentioned various drawbacks needs to be provided. Even if a mechanism is actuated only by one motor, instead of plural motors in conjunction with each other, the control that overcomes the above-mentioned various drawbacks is of benefit.
A need thus exists to provide a motor control device which is not susceptible to the drawback mentioned above.